CBA/N mice are an inbred strain of animals that exhibit an X-linked deficiency in immune responsiveness to certain carbohydrate antigens including dextrans. Isomaltodextrins derived by partial enzymatic or acid hydrolysis of dextran were coupled as haptens to the protein carrier keyhole-limpet hemocyanin and were used as immunogens. These glycoconjugates were used to study formation of antibodies that bind dextran in normal adult and neonatal mice and in mice with the CBA/N defect. Of particular interest are studies of the size requirements for an oligosaccharide hapten to elicit a cross-reactive antibody response to the native polysaccharide and the ontogeny of the response to the polysaccharide following immunization with a glycoconjugate.